This chapter is from the book

This chapter is from the book

Anyone who has even lightly ventured into developing detailed graphical
pro

Java 2D is probably the second most significant addition to the Java 2
Platform, surpassed only by the Swing GUI components. The Java 2D API provides a
robust package of drawing and imaging tools to develop elegant, professional,
high-quality graphics. The following important Java 2D capabilities are covered
in this chapter:

Colors and patterns: graphics can be painted with color gradients and
fill patterns.

Transparent drawing: opaqueness of a shape is controlled through an alpha
transparency value.

Local fonts: all local fonts on the platform are available for drawing
text.

Explicit control of the drawing pen: thickness of lines, dashing
patterns, and segment connection styles are available.

Transformations of the coordinate systemtranslations, scaling,
rotations, and shearingare available.

These exciting capabilities come at a pricethe Java 2D API is part of
the Java Foundation Classes introduced in Java 2. Thus, unlike Swing, which can
be added to the JDK 1.1, you cannot simply add Java 2D to the JDK 1.1. The Java
Runtime Environment (JRE) for the Java 2 Platform is required for execution of
2D graphical applications, and a Java 2-capable browser or the Java Plug-In,
covered in Section 9.9 (The Java Plug-In), is required for execution of 2D
graphical applets. Complete documentation of the Java 2D API, along with
additional developer information, is located at
http://java.sun.com/products/java-media/2D/.
Also, the JDK 1.3 includes a 2D demonstration program located in the
installation directory: root/jdk1.3/demo/jfc/Java2D/. In addition, Java
2D also supports high-quality printing; this topic is covered in Chapter 15
(Advanced Swing).

10.1 Getting Started with Java 2D

In Java 2, the paintComponent method is supplied with a
Graphics2D object, which contains a much richer set of drawing
operations than the AWT Graphics object. However, to maintain
compatibility with Swing as used in Java 1.1, the declared type of the
paintComponent argument is Graphics (Graphics2D
inherits from Graphics), so you must first cast the Graphics
object to a Graphics2D object before drawing. Technically, in Java 2,
all methods that receive a Graphics object (paint,
paintComponent, get_Graphics) actually receive a
Graphics2D object.

The traditional approach for performing graphical drawing in Java 1.1 is
reviewed in Listing 10.1. Here, every AWT Component defines a
paint method that is passed a Graphics object (from the
update method) on which to perform drawing. In contrast, Listing 10.2
illustrates the basic approach for drawing in Java 2D. All Swing components call
paintComponent to perform drawing. Technically, you can use the
Graphics2D object in the AWT paint method; however, the
Graphics2D class is included only with the Java Foundations Classes, so
the best course is to simply perform drawing on a Swing component, for example,
a JPanel. Possible exceptions would include direct 2D drawing in the
paint method of a JFrame, JApplet, or
JWindow, since these are heavyweight Swing components without a
paintComponent method.

Always call the paintComponent method of the superclass first,
because the default implementation of Swing components is to call the
paint method of the associated ComponentUI; this approach
maintains the component look and feel. In addition, the default
paintComponent method clears the off-screen pixmap because Swing
components implement double buffering. Next, cast the Grap_hics object
to a Graphics2D object for Java 2D drawing.

Pass in the Shape object to either the draw or
fill method of the Graphics2D object. The graphic context (any
paint, stroke, or transform applied to the Graphics2D object) will
define exactly how the shape is drawn or filled.

g2d.draw(someShape);
g2d.fill(someShape);

The Graphics2D class extends the Graphics class and
therefore inherits all the familiar AWT graphic methods covered in Section 9.11
(Graphics Operations). The Graphics2D class adds considerable
functionality to drawing capabilities. Methods that affect the appearance or
transformation of a Shape are applied to the Graphics2D
object. Once the graphics context is set, all subsequent Shapes that
are drawn will undergo the same set of drawing rules. Keep in mind that the
methods that alter the coordinate system (rotate, translate,
scale) are cumulative.

Useful Graphics2D Methods

The more common methods of the Graphics2D class are summarized
below.

public void draw(Shape shape)

This method draws an outline of the shape, based on the current
settings of the Graphics2D context. By default, a shape is bound by a
Rectangle with the upper-left corner positioned at (0,0). To position a
shape elsewhere, first apply a transformation to the Graphics2D
context: rotate, transform, tra_nslate.

This method draws the BufferedImage with the upper-left corner
located at (left, top). A filter can be applied to
the image. See Section 10.3 (Paint Styles) for details on using a
BufferedImage.

public void drawString(String s, float left, float bottom)

The method draws a string in the bottom-left corner of the specified
location, where the location is specified in floating-point units. The Java 2D
API does not provide an overloaded drawString method that supports
double arguments. Thus, the method call drawString(s,2.0,3.0) will not compile. Correcting the error requires
explicit statement of floating-point, literal arguments, as in
drawString(s,2.0f,3.0f).

Java 2D supports fractional coordinates to permit proper scaling and
transformations of the coordinate system. Java 2D objects live in the User
Coordinate Space where the axes are defined by floating-point units. When the
graphics are rendered on the screen or a printer, the User Coordinate Space is
transformed to the Device Coordinate Space. The transformation maps 72 User
Coordinate Space units to one physical inch on the output device. Thus, before
the graphics are rendered on the physical device, fractional values are
converted to their nearest integral values.

public void fill(Shape shape)

This method draws a solid version of the shape, based on the current
settings of the Graphics2D context. See the draw method for
details of positioning.

public void rotate(double theta)

This method applies a rotation of theta radians to the
Graphics2D transformation. The point of rotation is about (x,
y)=(0, 0). This rotation is added to any existing rotations of
the Graphics2D context. See Section 10.7 (Coordinate
Transformations).

public void rotate(double theta, double x, double y)

This method also applies a rotation of theta radians to the
Graphics2D transformation. However, the point of rotation is about
(x, y). See Section 10.7 (Coordinate Transformations) for
details.

public void scale(double xscale, yscale)

This method applies a linear scaling to the x- and y-axis. Values greater
than 1.0 expand the axis, and values less than 1.0 shrink the axis. A value of
-1 for xscale results in a mirror image reflected across the
x-axis. A yscale value of -1 results in a reflection about the
y-axis.

public void setComposite(Composite rule)

This method specifies how the pixels of a new shape are combined with the
existing background pixels. You can specify a custom composition rule
or apply one of the predefined AlphaComposite rules:
AlphaComposite.Clear, AlphaComposite.DstIn,
AlphaCompos_ite.DstOut, AlphaComposite.DstOver,
AlphaCompos_ite.Src, AlphaComposite.SrcIn,
AlphaCompos_ite.SrcOut, AlphaComposite.ScrOver.

The second approach permits you to set the alpha value associated with
composite rule, which controls the transparency of the shape. By default, the
transparency value is 1.0f (opaque). See Section 10.4 (Transparent Drawing) for
details. Clarification of the mixing rules is given by T. Porter and T. Duff in
"Compositing Digital Images," SIGGRAPH84, pp.
253259.

public void setPaint(Paint paint)

This method sets the painting style of the Graphics2D context. Any
style that implements the Paint interface is legal. Existing styles in
the Java 2 Platform include a solid Color, a GradientPaint,
and a Tex_turePaint.

public void setRenderingHints(Map hints)

This method allows you to control the quality of the 2D drawing. The AWT
includes a RenderingHints class that implements the Map
interface and provides a rich suite of predefined constants. Quality aspects
that can be controlled include antialiasing of shape and text edges, dithering
and color rendering on certain displays, interpolation between points in
transformations, and fractional text positioning. Typically, antialiasing is
turned on, and the image rendering is set to quality, not speed:

The Graphics2D context determines how to draw the outline of a
shape, based on the current Stroke. This method sets the drawing
Stroke to the behavior defined by pen. A user-defined
pen must implement the Stroke interface. The AWT includes a
BasicStroke class to define the end styles of a line segment, to
specify the joining styles of line segments, and to create dashing patterns. See
Section 10.6 (Stroke Styles) for details.

public void transform(AffineTransform matrix)

This method applies the Affine transformation, matrix, to the
existing transformation of the Graphics2D context. The Affine
transformation can include both a translation and a rotation. See Section 10.7
(Coordinate Transformations).

public void translate(double x, double y)

This method translates the origin by (x, y) units.
This translation is added to any prior translations of the Graphics2D
context. The units passed to the drawing primitives initially represent 1/72nd
of an inch, which on a monitor, amounts to one pixel. However, on a printer, one
unit might map to 4 or 9 pixels (300 dpi or 600 dpi).

public void setPaintMode()

This method overrides the setPaintMode method of the
Graphics object. This implementation also sets the drawing mode back to
"normal" (vs. XOR) mode. However, when applied to a
Graphics2D object, this method is equivalent to
setComposite(AlphaComposite.SrcOver), which places the source shape on
top of the destination (background) when drawn.

public void setXORMode(Color color)

This method overrides the setXORMode for the Graphics
object. For a Graphics2D object, the setXORMode method defines
a new compositing rule that is outside the eight predefined Porter-Duff alpha
compositing rules (see S_ection 10.4). The XOR compositing rule does not account
for transparency (alpha) values and is calculated by a bitwise XORing of the
source color, destination color, and the passed-in XOR color. Using XOR
twice in a row when you are drawing a shape will return the shape to the
original color. The transparency (alpha) value is ignored under this mode, and
the shape will always be opaque. In addition, antialiasing of shape edges is not
supported under XOR mode.